Overflow help
 

This is a simple simulation. There is a water tank with one outlet. I set up a source point in the middle of the tank to simulate the glycol leaking into the tank. The glycol is set by using an additional variable. The purpose is to know the flow rate of glycol at the outlet. However, when I run the solver,it showed that a wall has been placed at the outlet to prevent the water flow into the domain. And after several iterations it stopped with fatal overflow error.Can anybody tell me what's wrong?

p/s:If I setup an inlet instead of a source point. There was no error.